Radium implant to the parametrium in the treatment of Stage IIIB carcinoma of the cervix: analysis of dosimetry

Radium needle implant to the parametrium in order to supplement the dose rates to the cervix, parametrium and pelvic wall from a protruding intrauterine tandem was simulated using the skeleton of an adult pelvis in a water phantom. The results of direct dosimetry are presented. The parametrial implant approach was instituted in our clinic in 1975 to minimize local failures, especially parametrial, in Stage IIIB carcinoma of the cervix. The technique is used with patients who cannot accommodate two vaginal ovoids with the intrauterine tandem for conventional intracavitary radium therapy because of the extent of the neoplastic disease. Our dosimetric results showed an increase in the parametrial and pelvic wall dose rates of better than 60% with a typical implant of six half-intensity (0.33 mg/cm) needles to the affected parametrium; the bladder and rectum dose rates increased by less than 17%. There was a relatively minimal (8 to 13%) increase in the dose rates to other pelvic node-bearing sites. Results for a minimal implant to both proximal parametria and a clinical example of the parametrial implant application are also presented